1. Field of the Invention
The invention relates generally to wireless communication systems. More particularly, this invention relates to optimizing the allocation of the frequency spectrum among several stations of a wireless communication system.
2. Description of the Related Art
Wireless communication systems provide for the transmission and reception of voice, data, and video information among multiple stations (e.g., remote units) over radio frequency (RF) channels. The RF spectrum is limited by its very nature and, consequently, only a small portion of the spectrum can be assigned to a particular industry. Hence, in an industry such as the satellite communication or cellular telephone industries, designers are continuously challenged to efficiently allocate the limited spectrum to allow as many remote units as possible to have access to the assigned frequency spectrum.
One way of satisfying the demands of this challenge includes implementing one or more modulation techniques. Some modulation techniques, such as time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA), have demonstrated an efficient spectrum utilization. Each of these access techniques is well known in the art and, hence, will not be described herein. Generally, each of these techniques provides a method of accessing a particular segment of the spectrum by multiple contending remote units (e.g., users). These techniques, however, do not account or adapt for variations in propagation conditions when allocating a particular segment of the spectrum to the multiple users. For example, in a satellite system that employs a TDMA technique, a user is typically allocated a particular periodic timeslot (on a predetermined frequency) during which the user may communicate with a hub station. To allow multiple users to communicate with the hub station, multiple non-overlapping timeslots are allocated to multiple users, respectively. In nearly every wireless system, however, signal propagation may be subject to unpredictable degradation over one or more intervals of time. Generally, there are several physical phenomena which introduce degradation in the wireless medium. For example, in satellite communication systems, signal degradation may be caused by weather conditions (e.g., rain storms) or environmental interference. In land based communication systems, signal degradation may be caused by physical phenomena, such as multipath propagation and varying distance between the transmitter and receiver. Such signal degradation adversely affects channel performance for some users, but not necessarily for others.
Moreover, these sophisticated access techniques do not accommodate for or respond to changes in the utilization of the assigned spectrum among various users. For example, during a particular interval of time one user may be in need of transmitting an amount of information that, if transmitted with the current bandwidth, may take an unreasonable length of time. During the same interval of time, another user may not have such a need and be idle. This situation is particularly common in data communication networks, such as the Internet, where data is transmitted in bursts or packets (i.e., chunks of bits) between one communication station and another. The bursty characteristic of such networks renders conventional frequency spectrum utilization inefficient.
Therefore, there is a need in the industry to dynamically allocate frequency spectrum utilization in user demand and performance, so that all users have adequate access to the assigned spectrum.